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BUG: KCSAN: data-race in ____sys_sendmsg / fasync_insert_entry

read-write to 0xffff88810f3a6da8 of 4 bytes by task 27752 on cpu 1:
 fasync_insert_entry+0x120/0x150 fs/fcntl.c:1071
 fasync_add_entry fs/fcntl.c:1098 [inline]
 fasync_helper+0x5e/0xc0 fs/fcntl.c:1116
 sock_fasync+0x58/0xc0 net/socket.c:1526
 setfl fs/fcntl.c:76 [inline]
 do_fcntl+0xd5e/0xf80 fs/fcntl.c:477
 __do_sys_fcntl fs/fcntl.c:602 [inline]
 __se_sys_fcntl+0xb1/0x120 fs/fcntl.c:587
 __x64_sys_fcntl+0x43/0x50 fs/fcntl.c:587
 x64_sys_call+0x2844/0x3020 arch/x86/include/generated/asm/syscalls_64.h:73
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810f3a6da8 of 4 bytes by task 27744 on cpu 0:
 ____sys_sendmsg+0x247/0x580 net/socket.c:2669
 ___sys_sendmsg+0x195/0x1e0 net/socket.c:2738
 __sys_sendmmsg+0x185/0x320 net/socket.c:2827
 __do_sys_sendmmsg net/socket.c:2854 [inline]
 __se_sys_sendmmsg net/socket.c:2851 [inline]
 __x64_sys_sendmmsg+0x57/0x70 net/socket.c:2851
 x64_sys_call+0x27aa/0x3020 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000002 -> 0x00042002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 27744 Comm: syz.7.7588 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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